A construction for restricting or damping vibration of cables of a diagonal stress bridge is known in the art. Such a construction includes, as shown in FIG. 13, an anchor pipe 2 or protective pipe disposed at a position on a girder or tower of a bridge to which an end of cable 1 is connected. The anchor pipe 2 includes a flange 3 which encircles the cable 1. A plurality of visco-elastic bodies 4 are disposed between the flange 3 and the cable 1. Vibration of the cable 1 causes shear deformation in the visco-elastic bodies 4, so as to cause energy loss in the visco-elastic bodies 4, thus restricting or damping vibration of the cable 1 (see Japanese Patent Public Disclosure No. 06-136718 (KOKAI HEI-6-136718) and Japanese Patent Public Disclosure No. 07-3720 (KOKAI HEI-6-3720).
A diagonal stress bridge is constructed by first erecting main towers. Then, steel girders or girders of prestressed concrete are extended outwardly from the main towers. The girders are connected to and supported by the main towers using diagonal members (cables). Further girders are constructed in repetitive manner.
Thus, the amount of tension to be carried by the cables varies at a given time during the course from the initial stage to the completion of the construction work. Accordingly, the core of the cable 6 disposed centrally of the cables is caused to be offset from an intended position for design, or to be changed in its angle of inclination. In an actual large bridge, the amount of such an eccentricity may be even on the order of some tens millimeters.
Under the circumstances, the vibration damping device disclosed in Japanese Patent Public Disclosure No. 6-136718 or 7-3720 mentioned above is frequently difficult to be mounted between the anchor pipe 2 and the cable 1.
That is to say, the configuration of a visco-elastic body 4 is, in essence, determined by an expected spring constant or damping constant, and the thickness of the visco-elastic body is on the order of 20 to 80 millimeters. Thus, positional adjustment in the amount of some tens millimeters during mounting is not achieved by solely deforming the visco-elastic body.
In practice, the procedure of mounting the anchor pipe 2 on a girder 2 is delayed until the tension of the cable becomes unchanged as when the bridge is almost completed. Then, the longitudinal center of the anchor pipe 2 is aligned with the longitudinal center of the cable. This restricts fabrication work for girders and towers, or mounting work for the anchor pipes.